No-bypass filter system

ABSTRACT

A no by-pass filter system comprising a filter head, canister and filter element arranged to divide the canister into an upstream and a downstream side. Ports in the filter head direct fluid to and away from the filter element. Positioned in the flow path between the filter element and the outlet port is a device responsive to the differential pressure across the filter element for restricting flow and thereby maintaining the differential pressure substantially constant.

United States Patent Gaudet et a1.

[ Dec. 16, 1975 NO-BYPASS FILTER SYSTEM Inventors: Ronald M. Gaudet,Cheshire, Conn.;

Samuel S. Michell, Monroeville; Michael J. Kozy, Pittsburgh, both of Pa.

Schroeder Brothers Corporation, McKees Rocks, Pa.

Filed: June 10, 1974 Appl. No.: 477,982

Assignee:

US. Cl. 210/137 Int. Cl. B01D 33/40 Field of Search 210/137, 136, 130,133

References Cited UNITED STATES PATENTS 11/1930 Short 210/137 12/1966Quinting 210/136 X Primary Examiner-Frank A. Spear, Jr. Attorney, Agent,or Firm-Webb, Burden, Robinson & Webb [57] ABSTRACT A no by-pass filtersystem comprising a filter head, canister and filter element arranged todivide the canister into an upstream and a downstream side. Ports in thefilter head direct fluid to and away from the filter element. Positionedin the flow path between the filter element and the outlet port is adevice responsive to the differential pressure across the filter elementfor restricting flow and thereby maintaining the differential pressuresubstantially constant.

4 Claims, 4 Drawing Figures US. Patent Dec. 16, 1975 Sheet 1 0123,926,806

FIG.

FIG. 2

FIG.3

US. Patent Dec. 16, 1975 Sheet2of2 3,926,806

umDmmuma 2 umkma3 2d '9 ldV 'HHHSSHUd 'IVILNBHl-L-IIO lSd NO-BYPASSFILTER SYSTEM BACKGROUND Hydraulic systems which comprise reservoirs,pumps and work elements such as servo valves, hydraulic cylinders ormotors must contain suitable filters to maintain the contamination atsafe levels. The source of the contamination may include for example,solid particles from chemical breakdown of the fluid medium itself,contaminants created by pump cylinder and valve port wear and erosion,contaminants present when the hydraulic system is first started up andthose introduced during installation of new or additional elements tothe system or adding additional fluid to the system.

Hydraulic filters are generally comprised of a filter head or base towhich is secured a canister or bonnet. A filter element, generallytubular, is positioned within the bonnet. The filter head is shaped tobe connected to the inlet and outlet conduit. The filter head directsflow through the filter element.

As the filter element gathers dirt, the pressure drop across the elementrises. In a typical case, if the filter element is not replaced, thepressure rises to the threshold level of the pressure bypass valve whichbypasses the fluid around the filter element. In some applications, forexample, systems containing certain servo valves, it would be unsuitableto bypass the filter element for a period long enough for the fluid toreach a damaging contamination level. In these instances, because of thevery high pressure drops which may develop, high cmsh filter elementsare employed. These are extremely expensive relative to the throw awayfilter elements typically used in bypass systems.

It is an advantage of this invention to provide a nobypass filter systemwhich need not use high crush filter elements, but may use conventionalthrow away filter elements. It is a further advantage of this inventionthat the working elements of the no-bypass filter system are providedwithin the filter housing.

Briefly, according to this invention, the filter system is comprised ofthe conventional filter head, canister, and filter element. The filterelement is arranged to divide the canister into an inlet and outletside. The filter head has an inlet port for directing fluid to the inletside of the canister and an outlet port for delivering fluid from theoutlet side of the canister. The improvement herein comprises a devicewithin the filter head for maintaining a pressure drop across the filterelement constant. This device comprises a piston and hollow cylinderwhich moves therein. The piston and cylinder are both hollow cylinderseach with one closed end and one open end. The piston is arranged toslide within the cylinder such that closed ends of each are biased awayfrom each other. Inlet and outlet holes are provided in the piston andcylinder walls to allow flow through the piston and cylinder. The closedend of the piston cylinder is in communication with the inlet port ofthe filter head, that is, with the upstream pressure. As upstreampressure increases, due to increased pressure differential across thefilter element, the piston is forced to move against the bias within thecylinder. The relative movement of the piston and cylinder restrict theflow through the piston and cylinder. Hence, as the filter collectscontaminants the pressure at the inlet port increases and the pressuredrop across the filter element starts to increase. But, the relativemovement of the pistons and cylinder restricts the flow through 2 thepiston and cylinder thereby limiting the differential pressure.

Other objects and advantages of this invention will become clear from areading of the detailed description made with reference to the drawingsin which:

FIG. 1 is a section view of the filter system described herein;

FIG. 2 is a view of a suitable cylinder for use according to thisinvention;

FIG. 3 is a section view of a suitable piston for use with the cylinderdescribed in FIG. 2 and,

FIG. 4 is a graph showing the change in differential pressure as theupstream pressure increases in filter systems according to thisinvention.

Referring to FIG. 1, a filter system according to this inventioncomprises a filter head or block 1 and a canister 2 which are joinedtogether by a suitable means such as bolts and nuts 3 through flangesprovided therefor. Between the flanges, there is a gasket 4.

Within the canister is a filter element shown as a tubular filterelement 5 of the type well known in the filtering art. The filterelement is held in place by a spring 7 and end plate 8 at one end and acylindrical extension 9 of the filter head 1. The filter element isprovided with the sealing grommets 10 and 11 which prevent leakage pastthe filter element.

The filter head 1 has an inlet port 13 and outlet port 14. The filterhead is provided with a passage 15 which directs flow from the inletport 13 to the inlet side of the filter element. The filter head isprovided with a passage 16 for directing flow away from the outlet sideof the filter element through the outlet port 14.

Positioned between the passage 16 and the outlet port 14 is a device forlimiting the pressure drop across the filter element. The devicecomprises a piston 20 and a piston cylinder 30. A spring 40 holds theclosed end 21 of the piston 20 away from the fixed closed end 31 of thecylinder 30.

Referring now to FIG. 2, there is shown a suitable piston cylinderaccording to the teachings of this invention. The cylinder has an openend 32 and a closed end 31. The particular cylinder shown has threads 33on the exterior near the open end. The cylinder can be inserted in thefilter head 1 through the outlet port 14 and threaded into a positionprovided therefor. In that position, the open end of the cylinder is incommunication with the inlet port. A pair of ribs 34 are spaced aroundthe outer circumference of the cylinder for maintaining a seal, forexample, O-ring 35 in position. The ribs are positioned about midwaybetween the open and closed ends of the cylinder. Hence, when thecylinder is inserted in place in the filter head, fluid cannot flow fromthe outlet side of the filter element to the outlet port without passingthrough the cylinder. The cylinder is provided with a plurality of inletopenings 36 in the cylinder sidewall between the open end 32 and theribs 34. The cylinder is provided with a plurality of outlet openings 37positioned adjacent the closed end. These outlet openings cooperate withthe skirt of the piston as explained hereafter, to restrict the flow tothe outlet port.

Referring to FIG. 3, the piston may be a simple hollow cylinder with aclosed end 21. A plurality of inlet openings 26 are positioned about thecylindrical sidewall.

When the hollow piston is positioned within the cylinder, the closed end21 of the piston 20 is biased away from the closed end 31 of thecylinder 30 by a spring 40. The spring may be held slightly compressedin its most expanded position by the piston held by a ring 41 snappedinto a groove 42 on the inside of the cylinder near its open end. Whenthe piston is biased against the ring 41 it is in its open position;that is, the openings 36 in the cylinder and the openings 26 in thepiston are substantially aligned and the skirt of the piston does notoverlap the outlet openings 37 of the cylinder. The piston is shorterthan the cylinder to enable it not to obstruct the openings 37 when thepiston is in the open position.

In operation, the no-bypass filter operates to main tain the differencebetween the upstream pressure P1 and the inner element pressure P2substantially constant, or below the crushing strength of the filterelement. The downstream pressure P3 also remains substantially constant.In a typical filter system the differential pressure across the filterelement can increase almost indefinitely as the filter gatherscontamination from the fluid system. In the no-bypass system, accordingto this invention, the differential pressure rises, the piston moveswithin the cylinder 30 and thereby restricts the flow of fluid as theskirt of the piston moves over the outlet openings 37. The inner elementpressure P2 increases with the upstream pressure Pl due to restriction.As the element continues to collect dirt the differential pressureincreases to a critical point. That is, where the restriction caused bythe piston skirt is such that PI and P2 climb at a rapid rate until thesystem relief valve (not part of this invention) is opened; P1 and P2always increase together, thus maintaining a substantially constantdifferential pressure. Meanwhile, the downstream pressure remainssubstantially constant with no increase except with workload variation.

When P1 reaches the relief valve setting and flow is diverted away fromthe filter, but not around the filter, the piston remains at thecritical point until after the filter is changed. The system cannot bereturned to nonnal until the element is serviced. Set forth below inTables I and II are two test runs with the no-bypass filter according tothis invention in which the upstream pressure P1, the inner elementpressure P2 and the downstream pressure P3 were continuously monitoredat various time increments and recorded at various time increments, asthe filter element gathered contamination that had been intentionallyplaced in the system for the purpose of demonstrating the effectivenessof the no-bypass filter system.

TABLE Il-continued 5 GPM 1 2 3 4 5 6 7 P3 500 500 500 500 500 500 200AP1 & P2 4 31 34 35 35 25 Referring now to Table II, a higher pressureapplication is demonstrated. Again, it will be seen that as the filtergathers contaminants, the upstream pressure increases and thedifferential pressure across the filter element remains relativelyconstant. In this application, the upstream pressure climbed to thesystem relief valve setting which was 1000 psi. At this point, the valvedoes not return to the open position even though the differentialpressure drops off when the flow is diverted away from the no-bypasssystem. Flow must be completely cut off and the pressure relieved beforethe valve returns to the open position. This, of course, is highlydesirable as it prevents the continued use of the system with a dirtyfilter. In the case of cold starts, the system may have to be warmed upby intentionally diverting flow away from the no-bypass filter until thefluid temperature and viscosity are suitable to prevent the closing ofthe valve.

FIG. 4 shows a graph which demonstrates the relationship between theupstream pressure and differential pressure in a no-bypass filter systemaccording to this invention as the filter gathers contamination.

Having thus described my invention in the detail and particularity asrequired by the Patent Laws, what is desired protected by Letters Patentis set forth in the following claims.

We claim:

1, In a filter system for a fluid activated system comprising a filterhead, canister and filter element, said filter element arranged todivide the canister into an inlet and outlet side, said filter headhaving an inlet port for directing fluid to the inlet side of saidcanister and an outlet port for delivering fluid from the outlet side ofthe said canister, the improvement comprising a means for maintainingthe pressure drop across the filter element constant comprising a pistoncylinder having an open and closed end, a hollow cylindrical pistonpositioned in said piston cylinder having a closed end disposedgenerally at the open end of the cylinder and an open end disposedgenerally at the closed end of the cylinder, means for biasing theclosed end of the hollow piston away from the closed end of thecylinder, open- TABLE I 5 GPM I 2 3 4 5 6 7 8 9 IO ll I2 I PI 29 35 5O80 I25 I10 I25 I50 I P2 25 25 25 25 30 35 44 91 76 9I ll7 I44 P3 25 2525 25 25 25 25 25 25 25 25 25 API & P2 4 IO 20 25 30 35 35 34 33 33 3231 TABLE II 5 GPM 1 2 3 4 5 6 7 Pl 504 530 531 534 550 650 1000 P2 500500 500 500 515 615 975 ings being provided in the sidewall of thecylinder and the hollow piston for permitting flow into the piston andcylinder and openings being provided in the sidewall of the piston nearthe closed end for permitting flow out of the cylinder, said piston andcylinder arranged such that the outside of the closed end of the pistoncylinder is in communication with the inlet port and the piston andcylinder form part of the flow path between the outletside of the filterelement and the outlet port such that as the filter collectscontaminants the pressure at the inlet port increases and the pressure 6axis of the ports.

3. In a filter system according to claim 1, the cylinder having its axisaligned with the inlet port.

4. In a filter system according to claim 1, wherein the inlet and outletopenings of the cylinder and the hollow cylindrical piston are circular.

1. IN A FILTER SYSTEM FOR A FLUID ACTIVATED SYSTEM COMPRISING A FILTERHEAD, CANISTER AND FILTER ELEMENT, SAID FILTER ELEMENT ARRANGED TODIVIDE THE CANISTER INTO AN INLET AND OUTLET SIDE, SAID FILTER HEADHAVING AN INLET PORT FOR DIRECTING FLUID TO THE INLET SIDE OF SAIDCANISTER AND AN OUTLET PORT FOR DELIVERING FLUID FROM THE OUTLET SIDE OFTHE SAID CANISTER, THE IMPROVEMENT COMPRISING A MEANS FOR MAINTAININGTHE PRESSURE DROP ACROSS THE FILTER ELEMENR CONSTANT COMPRISING A PISTONCYLINDER HAVING AN OPEN AND CLOSED END, A HOLLOW CYLINDRICAL PISTONPOSITIONED IN SAID PISTON CYLINDER HAVING A CLOSED END DISPOSEDGENERALLY AT THE OPEN END OF THE CYLINDER AND AN OPEN END DISPOSEDGENERALLY AT THE CLOSED END OF THE CYLINDER, MEANS FOR BIASING THECLOSED END OF THE HOLLOW PISTON AWAY FROM THE CLOSED END OF THECYLINDER, OPENINGS BEING PROVIDED IN THE SIDEWALL OF THE CYLINDER ANDTHE HOLLOW PISTON FOR PERMITTING FLOW INTO THE PISTON AND CYLINDER ANDOPENINGS BEING PROVIDED IN THE SIDEWALL OF THE PISTON NEAR THE CLOSEDEND FOR PERMITTING FLOW OUT OF THE CYLINDER, SAID PISTON AND CYLINDERARRANGED SUCH THAT THE OUTSIDE OF THE CLOSED END OF THE PISTON CYLINDERIS IN COMMUNI CATION WITH THE INLET PORT AND THE PISTON CYLINDER FORMPART OF THE FLOW PATH BETWEEN THE OUTLET SIDE OF THE FILTER ELEMENT ANDTHE OUTLET PORT SUCH THAT AS THE FLTER COLLECTS CONTAMINANTS THEPRESSURE AT THE INLET PORT INCREASES AND THE PRESSURE DROP ACROSS THEFILTER ELEMENT ALSO INCREASES UNTIL THE CYLINDRICAL PISTON MOVES WITHINTHE PISTON CYLINDER TO RESTRICT THE FLOW OF FLUID FROM THE OUTLET SIDEOF THE FILTER ELEMENT TO THE OUTLET PORT, THUS PREVENTING FURTHERPRESSURE DROP ACROSS THE FILTER ELEMENT.
 2. In a filter system accordingto claim 1 in which the inlet and outlet ports are aligned and thecylinder is arranged therebetween with its axis aligned with the axis ofthe ports.
 3. In a filter system according to claim 1, the cylinderhaving its axis aligned with the inlet port.
 4. In a filter systemaccording to claim 1, wherein the inlet and outlet openings of thecylinder and the hollow cylindrical piston are circular.